The valve of an active breathing control (ABC) device can be driven by the output of the navigator channel of the MRI scanner, rather than by inference from a measured breath flow rate. Where the MRI scanner is integrated with a radiotherapy device, the MRI data can be used to trigger the enforced breath-hold by the ABC, and the radiotherapy delivered while the ABC valve is shut. If the MRI data pertains to the actual position of the tumor, then the ABC device will (in effect) hold the tumor at a precise and reproducible point for treatment.
